1. Field
The present disclosure relates to an organic light emitting display device (OLED) and a method of fabricating the same.
2. Description of the Related Technology
An OLED typically includes a substrate, an anode disposed on the substrate, an emission layer (EML) disposed on the anode, and a cathode disposed on the emission layer. In such an OLED, holes and electrons are injected into the emission layer when a voltage is applied between the anode and the cathode. The holes and electrons recombine with each other in the emission layer to generate excitons. When these excitons transition from an excited state to a ground state, light is emitted.
Full-color OLEDs may have emission layers, each emitting one of red (R), green (G) and blue (B) colors. However, the R, G and B emission layers in the OLEDs have different luminance efficiencies (Cd/A). The difference in the luminance efficiency causes the luminance of each emission layer to be different. The luminance is generally proportional to a current value. Accordingly, if the same current flows through emission layers of different colors, one color may have a lower luminance whereas another color may have a higher luminance. This makes it difficult to obtain proper color balance or white balance.
For example, since the luminance efficiency of a G emission layer is three to six times higher than those of R and B emission layers, more current needs to be applied to the R and B emission layers to achieve the white balance.
To solve this problem, a method has been proposed including forming an emission layer that emits light of a single color, i.e., a white (W) color, and then forming a color filter layer for extracting light corresponding to a predetermined color from the emission layer, or alternatively a color conversion layer for converting light from the emission layer to light of a predetermined color.
FIG. 1 is a cross-sectional view of one example of a top-emission OLED. Referring to FIG. 1, a substrate 100 is provided. A first electrode 110 including a reflective layer is formed on the substrate 100. A thin film transistor may be interposed between the first electrode 110 and the substrate 100. An organic layer 120 including an emission layer, which may have a single layer or multiple sublayers, is formed on the first electrode 110. In an arrangement in which a W emission layer and a color filter are used to realize a full-color OLED, the organic layer 120 may have a stacked structure of R, G, and B emission layers. A second electrode 130 is formed of a transflective or translucent material on the organic layer 120, thereby completing the OLED. The transflective material may have a transmittance of less than about 90%.
In the illustrated OLED, a resonance effect may occur because the second electrode is formed of a transflective material. Three peaks for R, G, and B light in the electroluminescence (EL) spectrum thereof may not be uniform because of the resonance effect, and thus the white light cannot be maintained. Also, light of different wavelengths may be emitted depending on a viewing angle due to the resonance effect. The resonance effect is significantly affected by the thickness of the organic layer. Thus, a wavelength band of light to be filtered varies depending on the thickness distribution of the organic layer, causing color and luminance to be adversely affected.